Rotary transformers have been utilized for coupling multi-phase systems. See, for example, U.S. Pat. No. 3,471,708 to Rauhut wherein a non-synchronous rotary machine has stator windings connected to a first three-phase power system grid and rotor windings connected to a second three-phase system grid. If the frequency of one system is different from that of the second system, a torque is exerted on the rotor in one direction or the other so as to cause rotation of the rotor at a rotational rate equal to the difference between the network frequencies.
In one example deployment of a rotary transformer, a rotary transformer system is connected to transfer electrical power between a first electrical system (e.g., first electrical grid) and a second electrical system (e.g., second electrical grid). In such deployment, one of the rotor assembly and the stator is connected (e.g., by three phase lines) to the first electrical system, and the other is connected to the second electrical system. A drive motor rotates the rotor assembly in response to a drive signal generated by a control system. The first and second electrical systems may have a differing electrical characteristic (e.g., frequency or phase). The control system can bi-directionally operate the rotary transformer system at a variable speed for transferring power from the first electrical system to the second electrical system or vice versa (i.e., from the second electrical system to the first electrical system). Further information concerning such example deployment and variations thereof are disclosed in the following, all of which are incorporated herein by reference in their entirety: U.S. Pat. Nos. 5,953,225; 5,742,515; 5,841,267 5,952,816; U.S. patent application Ser. No. 08/825,502; and U.S. patent application Ser. No. 09/443,220.
Rotating electrical machines such as the rotary transformer/converter discussed above are normally manufactured and designed at operating voltages of 4 kV to 25 kV. Such being the case, heretofore on each side thereof the rotating transformer/converter a transformer must be employed in order to connect to typical transmission level voltages of 15 kV to 400 kV.
A rotary transformer system obviates the need for transformers for connecting to a high voltage electrical system such as an electrical grid or the like by using high voltage cables as one or both of rotor windings and stator windings. The rotary transformer system is driven by an electrical machine.
Thus, in accordance with the present invention, the windings of at least one of the rotor and the stator are high power cables utilized to obviate employment of a transformer between the one of the rotor and the stator and one of the first electrical system and the second electrical system. In alternate embodments, the high power cables can be used for windings of one or both of the rotor and stator. The high power cables are capable of operation with greater than 30 kV, e.g., and may operate as high as 100 kV or even higher (e.g., 500 kV). In non-limiting, representative example embodiments, the high power cables are formed from one of cross-linked polyethylene and ethylene propylene rubber.